In one form of secondary or enhanced oil recovery carbon dioxide gas is forced through a number of injection wells into an oil bearing formation causing oil in the formation to migrate toward and collect in a production well. In recovering the oil collected in the production well a sucker rod pump or the like may be used. Such a pump typically is mounted within a string of production tubing extending into the oil at the bottom of the well and includes a series of one-way check valve structures located downhole below the level of oil collected in the well. One of the valves, the traveling valve, is located at the bottom of a lifting chamber carried on the lower end of the sucker rod and allows oil to flow into the chamber with each down stroke of the rod. The other valve, the fixed valve, is located below the traveling valve and allows oil to flow one-way into an inlet chamber thereabove from a collection chamber at the bottom of the tubing string. Accordingly, with each up stroke of the sucker rod, oil flows into tubing past the fixed valve as the oil above the traveling valve is lifted through the tubing toward the surface. On the down stroke, the oil in the inlet chamber above the fixed valve flows past the traveling valve into the lifting chamber with the fixed valve preventing the oil from flowing reversely from the inlet chamber into the collection chamber and back toward the formation.
To support the tubing string downhole against movement in rhythm with the reciprocating action of the sucker rod, a tubing anchor may be used in proximity of the traveling valve. Preferably, the anchor is secured to the well casing such as by means of slips with the tubing string in tension. This helps keep the tubing from buckling on the up stroke of the pump rod so as to avoid potential wear between the rod and the inside of the tubing.
Unfortunately, the use of carbon dioxide in secondary recovery can have a very corrosive effect upon the tubing and pump apparatus with which the produced oil in the production well comes into contact as the oil is being pumped toward the surface. To neutralize the corrosive effects of the carbon dioxide, an amine compound may be injected into the oil and, it is desirable that such anti-corrosive chemical be added to the oil in the vicinity of the pump inlet so that the chemical is drawn into and mixed with the oil being pumped upwardly as an incident to the reciprocating action of the sucker rod. In this way, the chemical is concentrated for use in the area where it is most needed so as to avoid having to use excessive quantities. One way of providing the chemical at the pump inlet is through the use of a separate chemical delivery line secured to the outside of the tubing string and leading from a supply source at the top of the well to an outlet port opening into the collection chamber in the well just beneath the fixed valve.